Recently, many studies have been worked on organic semiconductor devices using organic semiconductor materials as organic electron components (for example, organic electroluminescent (EL) devices, organic FET devices, thin film devices such as organic thin film transistor devices or organic thin film photoelectric converting devices). As a result of studies, some organic semiconductor devices have been put to practical use.
To be improved in their performance, it is important for the organic semiconductors to use an organic semiconductor material having an excellent performance. Accordingly, intensive searches and studies have been carried out for an organic semiconductor material excellent in light emitting property and/or carrier mobility, etc.
In general, a carrier transport ability is required in an organic electron material to be applicable to electric and electronic devices such as organic thin film transistors, etc. For example, the carrier mobility, which influences an efficiency in charge transport, is an important factor for the organic EL device in order to attain highly efficient light emission or low power driving. Furthermore, practical use of the organic FET devices cannot be realized without improvement in the carrier mobility, which directly influences switching speeds and performance of devices to drive.
Organic semiconductors are generally low in the carrier mobility, compared with silicon-based semiconductors. The low carrier mobility gives the organic semiconductors a low response speed. Albeit this has been a hindrance to the practical use of the organic semiconductors, new organic semiconductors have been developed recently, in which a mobility equivalent to that of amorphous silicon is realized.
For example, it was reported that pentacene, which is a polycyclic aromatic molecule consisting of five benzene rings condensed to align straightly, showed high mobility (0.1 to 1.0 cm2/Vs) equivalent to that of amorphous silicon. Because the performance of a pentacene-based TFT is largely dependent on the purity of pentacene, which forms an active layer, the pentacene-based TFT was realized by inevitably conducting sublimation refinement in vacuum or in hydrogen stream in plural times before the production of the device. [See, for example, Non-Patent Citation 1 (IEEE Electron Dev. Lett. 18, 87 (1997))]
Moreover, Non-Patent Citation 2 (Joyce G. Laquindanum et al. Adv. Mater. 9, 36 (1997)) reported that benzodithiophene dimer, that is, the dimer of benzothiophene monomer, showed a mobility of 0.04 cm2/Vs.
Furthermore, it was recently reported that a combination of thiophene and fluorene produced a material having a mobility of 0.14 cm2/Vs. [See, for example, Non-Patent Citation 3 (Z. Boa et al. J. Am. CHEM. Soc. 123, 9214 (2001)). Another recent report demonstrated that mobilities of a dimer or a trimer of anthracene were in the 0.1 cm2/Vs order. [See, for example, Non-Patent Citation 4 (Suzuki et al. Angew. Chem. Int. Ed. 42, 1159 (2003)). Moreover, electric field effect elements having a semiconductor layer made of a large condensed polycyclic aromatic compound such as ovalene, hexabenzocoronene, circumanthracene or the like, have been reported (Patent Citation 1: Japanese Unexamined Patent Application Publication, Tokukai, No. 2004-158709 (published on Jun. 3, 2004).